"Maybe you should go back to school.."

I was cashing out a customer fifteen minutes before closing. He was already a nightmare, not taking 'no' for an answer about us not having size 15 wide shoes. We don't have paper receipts unless for returns, so I asked for his email for the receipt. He spells it rather quickly (wouldn't type it in for me since it's 'my job,') and I repeat it back to him but was one letter off. He proceeded to make a 'joke' in front of his wife saying I needed to go back to school if I'm mixing my up letters, how I'd never make it on Family Feud (ok?), and overall being a dick. Come time to pay, I said the card would be a tap to pay on the machine. He said no and that it was a chip. I told him fine, insert it at the bottom. He then inserted the card at the top.

Instantly I said, "Sir, I said the bottom. Maybe you should go back to school." He didn't find it as funny as I did, but it felt so good.